Breech bolt with gauge members



1m 28,1949. A. KURT! 2,474,143

BREECH BOL'I WITH QAUGE MEMBERS Filed March 11, 1946 Patented June 28, 1949 cannon Bo-LTWITH GAUGE Alexander Kurti," Woodbury, Comp, assignor to- The Autoyre Company, Incorporated, Oakville, Comm, a corporation of Connecticut Application March" 11, 1946*, Serial No. 653,557

theedge of the cavity'beingcrimped or staked for further security, and the bottom" of the cup: being substantially the same-plane as the exposed' face 015- the base after chambering. Thecup encloses an anvil, there being percussion pellet or wafer oi detonating compound interp'osed between the inner face of the cup and the anvil. Suitable apertures in the anvil 'in com municating with an aperture in the base permit the force" of detonation of the pellet to explode: thecharge and to-fire the round.

Percussion" is effected by afiring pin usuallycarried by the-bolt, the nose of the pin striking the primer cup todeform the bottom thereof" againstthe anvil, the pellet therebetween being exploded' 'by such force. In order reliably to cf f'ect detonation, it is highly important that the primer be deformed or indented by the firing by a-pr ecisely predetermined distance. An insuflici'ently' or so-called "light struck primer may not detonate the pellet, whereas the other extreme, namely, over indentation of the cup,

may pierce the same and permit the gases of explosion not only of the percussion pellet, but also ofthe-charge tobl'ow' back and erode the firing pin.

It is possible; by over-driving the firing pin, to

shear" a portion of the cup to such a degreethat' the displaced' slug of metal may be blown back; Such-particles of metal will soon seriously affect proper operation, and this condition, togetherercsioit'oi the pin d'ueto heat, requires disassembly ofthe' gun for" renewal or renovation the defective" parts.

the: brassv oi -the cup rather soft, the: projectionoil 'the-nos'e against the cupmay cause anactuah flowing of the brass into the space intermediate the nose and-the: aperture. in the bolt through .whichothe nose 'projects; The extruded metah:

Even afewimproperly indented-'- primers occurring during a' single burst of 'fire may result" in the misiunctioni ng' just gree of control over the depth of penetration of'the primer ma be achieved. However, front] the practical standpoint of producing gunsirr although inconsequentia as a result of a single such extrusion, may", after repetition, so clog't'h'e said space between the nose and aperture as to affect proper operation.

Certain types of automatic guns depend for repeated fire upon the force of the gases of ex; plosion of the charge or upon recoil to operate the mechanism, so that failure of a particular round to fire will'put the gun out of action, and

manual or pneumatic: recharging becomes necessary to extract the unexploded round an'd'to re commence automatic fire. Accordingly, a light struck" primer may result in failure to detonate,

and the unexploded: cartridge will terminateautomaticoperation of" the gun.

Prior to my invention, several ways of overcoming light struck or pierced primers have of the bolt when the latter is closed. Thus, by establishing accurate head space and similarly accurate locating the nose of the firing'pin with relation to the base of the cartridge, some dequantity production; maintenance of manufacturing tolerances is not always easy. Additionally; even though head space of a particular gun may be accuratelydeterm-ined when the gum leaves the factory, the insertion of a new barrel having dimensions oniyslightly at variance with the expended barrel willdeterm-ine a dififerent" head space with the difficulties consequent there-- from.

relating dimensions of several parts.

accurate machining" of the inner end face ofthe barrel with respect to the receiver, of the bolt,-

the firing pin, the breechblock slides, andof the breec'hblock' slide key; Obviously, an accumula- *"ti'onof errors in dimensions, inconsequential of themselves, may, in toto, cause serious variation in head space.

Another cause of inaccurate indentation of the primer may reside in variations between the di-" ameter' of the cartridge casing and the corre-' sponding aperture of thebreech, It willbecor-m 'pre'hended that the casing is frequently tapered; and? the breech opening likewise. Thus; even extremely minute departures from specified di ameters for the casing wili' result in the car- 3 tridge being chambered too far into the breech or not far enough, the degree of longitudinal displacement being many times the amount of diametral error, due, of course, to the tapered mating surfaces.

In some prior guns attempts were made to control the degree of penetration by balancing the kinetic energy of the firing pin against the resistance of the primer cup. It will be apparent that little, if any, reliability could be attached to such means, for, if lubrication varied, friction of the firing pin in its guide would affect penetration, and variations in the composition of the metal of the cup would likewise yield unpredictable functioning.

Having in view the many factors resulting in improper indentation of the primer cup, my invention has for its principal object the provision of means associated with the bolt of a firearm and so constructed and arranged as to fix the distance to which the firing pin may indent the primer cup, such means being independent of all factors other than the bolt, firing pin, and base of the cartridge.

A further object is to provide means for the purpose aforesaid comprising a gauge pin or pins of predetermined length carried by the bolt and having the end faces of the pin or pins adapted to abut the base of the cartridge casing and a selected surface of the firing pin, respectively.

Another object is to provide a gauge pin or pins as aforesaid having a contour at the end thereof protruding from the face of the bolt such as to prohibit fouling of a cartridge thereon.

An additional object resides in the provision of a gauge pin or pins as pointed out which shall be simple in construction, easily installed or replaced, and trouble-free in operation.

Other and further objects will appear from the accompanying description and drawing, in which latter:

Fig. 1 is a fragmentary plan view partly in cross section through the axis of the barrel and bolt of a gun or firearm embodying my invention;

Fig. 2 is an elevational View taken on the line 22 of Fig. 1; and

Fig. 3 is a detail perspective view of one of the gauge pins shown in Figs. 1 and 2.

By way of exemplification, my invention will be described in connection with a gun of a wellknown type having a barrel including a breech or chamber for reception of the round, a bolt for chambering the round and reciprocable in a suitable guide, and a firing pin cooperative with the bolt for detonating the primer. It will be understood from what follows, however, that I do not intend to limit the invention to a gun of any particular type, except that it comprise at least the principal elements aforesaid.

Referring to Figs. 1 and 2, the bolt is indicated at ill, the firing pin at H, and the barrel at 12. The bolt if! is shown in forward position and at the instant following chambering of the round [3 thereby. Immediately thereafter the firing pin H moves forward to strike the primer, the driving spring I4 carrying the bolt and firing pin simultaneously forwardly, so that immediately after chambering, the firing pin may be moved by the spring [4 relatively to the bolt H] to indent the primer, as is understood by those skilled in this art.

Limit of forward movement of pin ll may be determined by various means, for example, by a key engaging a slot disposed on one side of the pin I I, the key being also engaged with the bolt, or by any equivalent means. Usually clearance is afforded between the cooperating elements of the pin and bolt in order to permit the pin to move forwardly by the amount of such clearance and as indicated at A, the dotted line at dimension A indicating the rear face of the firing pin after it has moved to primer-indenting position. In prior guns the distance A fixed to some extent the depth to which the nose I6 of the pinl I could indent the primer. However, in my improved construction such clearance A is not depended upon, the proper depth of penetration of the nose It being the result of means now to be described.

In the face of the bolt I0 (Fig. 2) and in alignment with the axis thereof, is provided a pair of cylindrical apertures H, of a depth sufficient to permit gauge pins i8, slidably movable therein, to occupy proper operative position with respect to the front shoulder IQ of the pin I i.

The extension of the pin H from the shoulder iii to the tip of the nose i6 is indicated at B, and the length of the gauge pins !8 at C. Dimension D is relatively inconsequential and merely indicates the amount by which the outer face of the primer cup 28 is depressed below the face 2! of the base of the cartridge e. g., for a 0.60 caliber round dimension D is 0.010".

Proper penetration of the cup 253 is achieved when the inner face 22 thereof is pushed against the tip of the anvil 23. In imparting the proper percussive efiect to the detonating pellet 24, the cup 20 is not pierced and the primer is not light struck.

To establish a penetration E, the dimensions B and C are so related that the difference B minus C is equal to the distance E. In Fig. 1 it will be noted that the nose It is just touching the cup 28 and is ready to indent the same. Accordingly, further movement of the firing pin H is limited by the length C, the firing pin when fully forward having its shoulder i9 abutting the face 25 of the pins l8, and the other face 26 of the pins abutting the face 2| of the round. Thus the firing pin is positively limited in its penetrating movement in accordance with the dimension C.

It will be obvious that the length of the gauge pins 88 may be varied, depending upon the dimensions of the parts co-operative therewith. Moreover, it will be apparent that the length of the pins may be easily held to very close tolerances in manufacture. Thus the problem of attempting to preserve a number of precise dimensions, as hereinbefore referred to, is eliminated in favor of only two dimensions, namely, B and C.

It will be noted that the pins I8 are free for axial sliding in order to take up their proper position with respect to the surfaces [9 and 2|. Under rapid-fire conditions it is conceivable that, due to inertia effect, the forward end of the pins will sometimes project from the face of the bolt, and to prevent fouling of a cartridge by lodgment against such projecting ends, the latter are preferably chamfered at 3| (Fig. 3). Accordingly, should the base of a cartridge strike a protruding pin [8, the same is cammed inwardly of the bolt by reason of the surface 3! and is free of the round.

In order to maintain a predetermined circumferential position of the pins l8 with surfaces 3| uppermost, they are preferably made of such diameter as to overlap the bushing 32 serving to guide the nose [6 (Fig. 2), and arcuate notches 33 adapted to slidably engage the circular periphery of the bushing are provided. In this manner pins 3 are keyed against rotation. Moreover, the rear face 34 of each of the notches 33 is adapted to engage the adjacent rear face of the bushing 32 and is hence retained against dissociation from the bolt I during the rapid reciprocations thereof.

It is not intended that the invention be limited to the form shown and described, nor to the quantity of pins l8. In some cases one pin may be found sufficient, and in others more than two. Moreover, the pins may be square or of other polygonal cross section, and guided in correspondingly shaped openings to preserve the desired circumferential position thereof, the essence of the invention residing in the provision of gauge pins of predetermined length intermediate the firing pin and base of the round.

From the preceding description it will have been observed that I have eliminated the possibility of a light struck primer, a pierced primer, or an extruded primer.

In certain guns in which my improvement has not been incorporated, the breechblock slides connected by means of a breechblock slide key can move on the bolt. The breechblock slide key, upon reaching the limit of forward travel, strikes the front face of the key slot in the bolt. Thus steel strikes steel, and the rebound of the slides evinces itself in poor functioning of the gun. However, with my improvement, the pins 18 strike the casing of the round prior to the breechblock slide key abutting the bolt, and the shock of contact is absorbed by the relatively softer brass. Hence the breechblock slides remain in their intended forward position.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

Having thus described my invention, what I claim and desired to secure by Letters Patent is:

1. In a firearm adapted to fire cartridges having a base-mounted primer, the combination comprising a bolt, a firing pin carried within the bolt and slidable with respect thereto, said pin having a nose arranged to indent the primer for detonation, said bolt having a front face for abutment with the base of the cartridge and an aperture providing a passage for projection of said nose beyond said face, said pin having a shoulder defining a forwardly disposed abutment, a plurality of gauge members carried by the bolt, said bolt having apertures opening through said face, one individual to each said member, and each member being slidable in its aperture, one end face of each member abutting said abutment and the opposite end face of each member being adapted to abut the base of a chambered cartridge, the dimension of each member being such that when the several related abutting surfaces are in contact, the said nose is at maximum indenting depth.

2. In a firearm adapted to fire cartridges having a base-mounted primer, the combination comprising a bolt having a face for abutment with the base of a cartridge for chambering the cartridge, a firing pin associated with said bolt and slidable with respect thereto, said pin having a nose for indenting the primer and an abutment portion, a gauging member interposed between said pin and the base of the chambered cartridge and having its opposite end faces adapted to abut said portion and base to determine the degree of indentation of the primer, said bolt having a guiding aperture for said member, and said member having a cam surface adjacent its forwardly disposed said end for engagement by a cartridge about to be chambered.

3. In a firearm adapted to fire cartridges having a base-mounted primer, the combination comprising a bolt having a face for abutment with the base of a cartridge for chambering the cartridge, a firing pin associated with said bolt and slidable with respect thereto, said pin having a nose for indenting the primer and an abutment portion, a cylindrical gauging member interposed between said pin and the base of the chambered cartridge and having its opposite end faces adapted to abut said portion and base to determine the degree of indentation of the primer, said bolt having a guiding aperture for said member, said member having a cam surface adjacent its base-abutting end for engagement by a cartridge about to be chambered, and said member and bolt having interengaging means for preventing rotation of said member about its axis.

4. In a firearm adapted to fire cartridges having a base-mounted primer, the combination comprising a bolt having a face for abutment with the base of a cartridge for chambering the cartridge, a firing pin associated with said bolt and slidable with respect thereto, said pin having a nose for indenting the primer and an abutment portion, a cylindrical gauging member interposed between said pin and the base of the chambered cartridge and having its opposite end faces adapted to abut said portion and base to determine the degree of indentation of the primer, said bolt having a guiding aperture for said member, and said member having a concave portion on one side thereof and said bolt having a convex portion means for preventing rotation of said member about its axis.

ALEXANDER KURTI.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,693,530 Spencer Nov. 27, 1928 1,993,887 Kewish Mar. 12, 1935 2,401,616 Clarke June 4, 1946 FOREIGN PATENTS Number Country Date 238,531 Germany Sept. 29, 1911 

